1. Field of the Invention
The present invention relates to an Internet Protocol (IP) telephony method for causing a telephone conversation to take place between two IP telephone terminals through a proxy and a router using an IP packet that includes a voice packet, and a system thereof.
2. Description of the Related Art
Following the development of Internet-related technologies, the IP telephony using the Internet has become popular. This IP telephony establishes a voice conversation according to a protocol such as real-time transport protocol (RTP) when a communication line has been established by performing signaling according to a protocol such as session initiation protocol (SIP) or H. 323.
Prior art literatures related to the present invention are as follows: JPA-H11-205475, JPA-2000-286882 and JPA-2003-46665.
The currently popular IP telephony is premised on the fact that one IP telephone terminal is connected to one router disposed in a company or an ordinary household.
Namely, when an IP telephony call arrives, the router establishes a correspondence between a pair of a global IP address and a global port number, and a pair of a local IP address and a local port number using a network address translation (NAT) technique or an IP masquerade technique. The correspondence is kept while an IP telephony communication takes place.
A plurality of IP telephone terminals are connected to a local area network (LAN) to which the router belongs. At present, however, there has been proposed no method for transferring the IP telephone communication from one IP telephone terminal to another IP telephone terminal.